Conventionally, viewing of stereoscopic images with stereoscopic image glasses having liquid crystal shutter lenses is achieved by displaying right-eye and left-eye images in sequence on an image display device of a TV (television) or of a PC (personal computer) and repeating an operation of, while a right-eye image is being displayed, opening only a liquid crystal shutter provided for a right-eye lens and, while a left-eye image is being displayed, opening only a liquid crystal shutter provided for a left-eye lens.
Specifically, as shown in FIG. 4, a radio signal transmitter 101 receives, from an image display device 106 of a TV or of a PC, (i) synchronizing signals for switching between right-eye and left-eye images and (ii) liquid crystal shutter control data indicating whether the right-eye or left-eye image is displayed and containing liquid crystal shutter control timings. The radio signal transmitter 101 transmits the synchronizing signals and the liquid crystal shutter control data in the form of radio signals via IR (infrared radiation) or RF (radio frequencies) as shown in (a) of FIG. 5. These pieces of information are received by a radio signal receiving section 111 of stereoscopic image glasses 110. Every time the radio signal receiving section 111 receives synchronizing signals, a liquid crystal shutter control signal timing generating section 112 of the stereoscopic image glasses 110 generates timings according to which liquid crystal shutters 114 of the stereoscopic image glasses 110 are controlled. Then, in accordance with the signals thus received, a liquid crystal shutter control section 113 of the stereoscopic image glasses 110 controls the liquid crystal shutters 114 for right-eye and left-eye lenses, respectively. This makes it possible to present right-eye and left-eye images separately to the right and left eyes of a viewer. This allows the viewer to view stereoscopic images.
This operation is described below with reference to timing charts shown in (a) through (d) of FIG. 5.
As shown in (a) of FIG. 5, the radio signal transmitter 101 transmits synchronizing signals each indicating a display update on the TV or PC image display device. Next, when a right-eye image is displayed, the radio signal transmitter 101 wirelessly transmits a “right shutter open” signal. Meanwhile, when a left-eye image is displayed, the radio signal transmitter 101 wirelessly transmits a “left shutter open” signal.
Meanwhile, as shown in (b) through (d) of FIG. 5, upon receiving the radio signals, the stereoscopic image glasses 110 output lens control signals for the right-eye and left-eye lenses, respectively, at optimal timings based on the synchronizing signals. Specifically, upon receiving the “right-eye shutter open” signal, the stereoscopic image glasses 110 output a lens control signal so that the liquid crystal shutter 114 for the right-eye lens opens. Further, upon receiving the “left-eye shutter open” signal, the stereoscopic image glasses 110 output a lens control signal so that the liquid crystal shutter 114 for the left-eye lens opens.
According to the conventional art described above, the radio signal transmitter 101 transmits radio signals at the timing switching between frames of the TV or PC display. For example, at a frame frequency of 100 Hz, the radio signal transmitter 101 transmits radio signals every 10 ms, and the stereoscopic image glasses 110 repeat reception of such radio signals at the same timing. This results in such a tendency that the higher the frame frequency becomes, the larger amount of power the radio signal receiving section 111 comes to consume.
Also, while the radio signal transmitter 101 has an always-on connection with a power supply of the television, the stereoscopic image glasses 110 are work on batteries. Thus, such a problem exists that as an increase in frame frequency leads to a decrease in the length of time that the stereoscopic image glasses 110 will continue to work.
In order to avoid such a problem, Patent Literature 1 discloses a radio signal receiving device for use in stereoscopic image glasses.
In order to solve the foregoing problem, the radio signal receiving device of Patent Literature 1 includes: a switch for turning on and off a power supply circuit of a receiving section; and means for controlling the switch. For example, even while receiving radio signals every 10 ms as mentioned above, the radio signal receiving device reduces power consumption by turning off the switch during an idle period between radio signal transmissions. Specifically, the radio signal receiving device detects the period of a radio signal sent from the transmitting end, calculates an idle period between radio signal transmissions, and turns off the switch during the idle period.